This invention relates, in general, to a method of forming an optoelectronic device, and more particularly, to a method of forming an optoelectronic device encapsulated in a cast polymer.
An optoelectronic device or coupler comprises an optical emitter and an optical receiver encapsulated in a discrete package. The optical emitter is comprised of a light emitting diode which is electrically coupled to an substrate or lead. The optical emitter is electrically isolated from the optical receiver. The optical receiver is comprised of a light sensing diode which is electrically coupled to an substrate or leadframe. The optical emitter and optical receiver are encapsulated in a transparent epoxy. An opaque, light reflective mold compound further encloses the optical transmitter and optical receiver and transparent epoxy in order to reflect light emitted from the transmitter back to the optical receiver and to protect the optoelectronic device from mechanical damage. The method of using a light reflective opaque epoxy is disclosed in U.S. Pat. No. 4,645,554, issued to Adams et al. on Feb. 24, 1987, and which is hereby incorporated by reference.
Another way of forming the optoelectronic device is by replacing the light reflective epoxy with a thin reflective layer over the transparent epoxy and then an opaque epoxy encapsulating the reflective layer. This process was disclosed in U.S. Pat. No. 5,329,131, entitled "Opto-electronic Coupler Having Improved Moisture Protective Housing", issued to Wijdenes et al on Jul. 12, 1994, and which is hereby incorporated by reference.
The disadvantage of the above devices is that the light which is reflected from the emitter to the receiver is not consistent because of the geometry or shape of the transparent epoxy which is used to form the reflective material thereon. The transparent epoxy is dispensed on the surface of the optical emitter and optical receiver and allowed to take its natural shape. Thus, the reflective material formed thereover does not have an optimum or consistent shape.
It would be desirable to form the transparent epoxy so that the reflective layer thereover is formed in a consistent and repeatable fashion to optimize the reflection of the light emitted from the optical emitter and to the optical receiver. Optimized and consistent transmission of light results in optimized and consistent electrical characteristics of the optoelectronic device.